1. Field of the invention
This invention related to a femoral component of a replacement hip joint of the "Exeter" type which has a collarless stem including a shoulder for fixing in a medullary canal by cement.
2. Discussion of Prior Art
The "Exeter" type femoral component of the kind shown in British Patent No. 1 409 054 is well known and comprises a neck which carries a ball head for cooperation with an acetabular socket. The neck is connected to a tapered collarless stem. Thus, there is no collar for resting either on the bone or the cement in the area where the stem joins the neck of the implant. This type of stem has evolved so that the stem can be given a highly polished finish to help it slide down inside the bone cement and the present invention relates to this type of femoral component.
In certain circumstances, it can be difficult to locate the femoral component in the medullary socket with the neck and ball at the precise height and angle required. This can be caused by the bone which are structurally imperfect or by difficulties in reaming a suitable cavity. It is particularly pronounced when cavities have to be lined with bone fragments prior to cementing or when there are irregularities and the present invention is intended to overcome some of the difficulties experienced.
It is known from U.S. Pat. No. 5,931,871 to provide a femoral component with a separate proximal component but in this application, the angle of the proximal component with regard to the stem about a proximal/distal axis is fixed and there is no provision for adjustment.
U.S. Pat. No. 4,051,559 also shows the use of a separate proximal component and this is provided to allow it to be placed in position on a cylindrical stem which is intended to be screwed directly into the bone. The proximal component is provided with a collar which is intended to rest against the cut and prepared bone and there is no provision for a stem to slide down inside bone cement as is required by the Exeter type hip stem. Moreover, the angular adjustment about a proximal/distal axis may be too coarse to allow final accurate adjustment with an Exeter type component.